First thing is to find your body shape. There are lots of style guides to recommend flattering clothes to show off your better qualities.

Maybe browse the secondhand stores in your area like Good Will. I know some church's in my locale also do the secondhand stuff for super cheap (I bought my nephew a Halloween costume for $1).

I love Savers the most, though. I'm not sure if they're nationwide or just in New England, but they're reasonably cheap and their donated items are sometimes unopened stuff.

Good luck finding a dress!

@Saeyra: This chart makes me feel awkward because I don't quite fit any of those body types. I have the waist of neat hourglass with the hips and thighs of full hourglass, bust of lean column, and shoulders of inverted pear...

@Miss Kitty: I wish I could offer more help, but tbh, 90% of dresses that I have bought have been on Amazon. And for those, I take my measurements and compare them with the measurements on the seller's size chart to get the best possible fit. Hopefully you find something that works well though! And good luck!